How does this solution sound to you?If you can plug things to the router, then get an off the shelf NAS. It would be easier to setup and manage. However, if you want one, which connects wirelessly to your router, then you need to build one. Essentially NAS is nothing but a computer with software meant to manage data.
I install a repeater in the first floor in computer room and hook it up to WIFI network.
Then I hook up the NAS device to LAN port of the repeater.
I am presuming the speed of the NAS won't be at par as compared to direct hooking it up with router but still it should be workable.
I am trying to do all this to avoid placing NAS next to WIFI router.
Wifi Router at my place is at ground floor behind TV mount+stand and other devices like ipTV, VOIP Landline phone etc are already hooked to the router.
Also, I want to place it such a way so that it is non reachable to my naughty 5 year old son